Absolute permissive block system of railway signaling



May 26, 1942.

R. R. KEMMERER .ET'AL ABSOLUTE PERMIS SIVE BLOCK SYSTEM OF RAILWAY SIGNALING Filed April 5, 1941 s Shets-Sheet 1 SE T 216' I F s E a mp w n 0 Z mmd m 2 4 r 0 M n (W T m R u. m m 5 m 4 m F flllxlllrul| 1? 8 9 m m y 1942- R. R. KEMMERER ETAL 1 2,283,998

ABSOLUTE PERMISSIVE BLOCK SYSTEM 0F RAILWAY SIGNALING Filed April 3, 1941 8 Sheets-Sheet 3 IYNVENTORS .hgmmerer and CPa M15. Szapler.

' 7215112 ATTO NEY R. R. KEMMERER ETAL 2,283,998

ABS OLUTE PE RMISSIVE BLOCK SYSTEM OF RAILWAY SIGNALING May 26, 1942.

Filed April 3, 1941 8 Sheets-Sheet 4 INV ENTORS and Stapler.

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ABSOLUTE PERMISSIVE BL OCK SYSTEM OF RAILWAY"SIGNALING Filed April 3, 1941 8 sheets sheet 8 "INVENTO RS filplzil zznmem aad 725E111 ATTORNEY Patented May 26, 1942 ABSOLUTE PERMISSIVE BLOCK SYSTEM F RAILWAY SIGNALING Ralph R. Kemmerer, Swissvale, and Crawford E. Staples, Edgewood, Pa., assignors to The Union Switch & Signal Company,-Swissvale, Pa., a corporation of Pennsylvania Application April 3, 1941, Serial No. 386,632

29 Claims.

Our invention relates to absolute permissive block (A. P. B.) signaling systems for stretches of two-direction running railway track and it has special reference to systems of this character wherein all major functions of both wayside and cab signal control are performed without the aid of line wires and by means of coded energy that is transmitted through the track rails.

Generally stated, the object of our invention is to improve the organization and broaden the range of application of coded track circuit A. P. B. systems which use the coded feed back operating principle of Frank H. Nicholson Patent No. 2,021,944 (issued November 26, 1935) and which are exemplified by the following copending applications of common ownership herewith: (1) Serial No. 294,897 filed September 14, 1939, by Ralph R. Kemmerer; (2) Serial No. 315,801 filed January 26, 1940, by Crawford E. Staples; and (3) Serial No. 382,431 filed March 8, 1941, by Frank H. Nicholson,

A more specific object is to make an improved utilization of the principles of track circuit reset that are disclosed and claimed by: (1) a copending application Serial No. 386,642 filed April 3,

1941, by Robert M. Gilson; and (2) a copending application Serial No. 386,615 filed April 3, 1941, by Leslie R. Allison. I

Another object is to make an improved application of certain train detecting and cab signal supply apparatus that is disclosed and claimed by a copending application Serial No. 383,571 filed March 15, 1941, by Ralph R. Kemmerer.

We shall describe one representative form of A. P. B. signaling apparatus that embodies our invention and shall then point out the novel features thereof in claims. This illustrative embodiment-is disclosed in the accompanying drawings in which:

Figs. 1a to If, inclusive, are diagrammatic views which when placed end to end in the order named represent a stretch of two-direction running railway track that i's-equipped with A. P. B. sgnaling apparatus which incorporates our improvements; I

Fig. 2 is a single line diagram showing the limits of track circuit control for each of the several wayside signals with which the singletrack To facilitate description of the various circuit diagrams of these views it will be assumed that the left end thereof is west and the right end is east. Hence, train movements in the direction of from left to right will be spoken of as eastbound and movements in the direction of from right to left will be spoken of as westbound."

Referring first to the composite diagram of Figs. la-lf, the improvements of our invention are there disclosed in a system of absolute permissive block (A. P, B.) signaling for a stretch of main line track I2 which extends from a west passing siding PSI (Fig. 1a) to an east passing siding PS2 (Fig. 1f) and'over which traffic may move in either direction. The usual insulated joints 3 divide the rails I and 2 of this stretch into.the customary plurality of successive track sections III, II-III, III-IV, IVV and V-VI and the rails of each of these sections form part of a coded track circuit combination later to be described.

The track and signal layout of Fig. 1

Wayside signals SE positioned at the sectiondividing locations, I, III, IV and V govern the passage of eastbound trains into and through the single track stretch IVI of Fig. 1. Of these eastbound devices, signals SEM and SES at the stretch west end I respectively control movements of eastbound trafiic from the westwardly extending main track l2,into the stretch and from the siding track PSI into the stretch. Device SES will, therefore, be designated as an eastbound siding leaving signal. By the same token device SEM might logically be called a main line leaving signal. For reasons later made evident, however, it will be referred to as the eastbound headblock signal.

Signals SEIII and SEIV at locations III and IV are the usual "eastbound intermediate devices and will be so referred to throughout this specification. Signal SEV at location V has similar intermediatecharacteristics but because of admitting eastbound traflic into the passing zone which siding PS2 defines it will be termed an eastbound siding entering signal,

Other wayside signals SW positioned at the section-dividing locations VI, IV, III and II govern the passage of westbound traffic into and through the single track stretch VI-I of Fig. 1. Of these westbound devices, signals SWM and SWS at the stretch east end VI respectively control movements of westboundtraflic from the eastwardly extending main track l-2 into the stretch and from the siding track PS2 into the stretch. Device SWS will, therefore, be designated as a "westbound siding leaving signal. Even though device SWM might logically be called a "main line leaving signal it will,'for

- SWIII at location II has similar intermediate characteristics but because of admitting westbound tramc into the passing zone which siding PSI defines it will be termed as a westbound siding entering" signal.

In the track and signal layout of Figs. la-lf each of the sections I-II and VIV of headblock track is relatively short and typically will have a length not exceeding two or three hundred feet. These headblock sections, together with the signals directly associated therewith, serve to increase the effectiveness of the directional protection that can be provided by an A. P. B. system wherein they are incorporated.

The intermediate" sections II--IH, III-IV and IV-V of the single track stretch are, how- 'ever, of the relatively longer order which the requirements of train braking make necessary. For a system layout of the represented two intermediate location (III and IV) type, each of the three intermediate sections just named typically will have a length of from one to two miles. As the number of intermediate locations is increased this length may, of course, be decreased; as the number of intermediate locations is decreased the section length must, by the same token, be proportionately increased.

A better conception of these comparative headblock and intermediate section lengths may be (The Fig. 1 plan of 4. P. B. signal control The eastbound and westbound wayside signals SE and SW earlier described for the mainline and passing siding tracks of Fig. 1 may, of course, be of any suitable form; as here shown each is of a well-known color light type which comprises three lamps G, Y and R. When selectively lighted these lamps respectively display the indications of green or clear, yellow or approach and red or stop.

Selecting the indication that each of these wayside signals displays are home" and distant control relays H and D. at the location of the signal. The relays in 'each of these control sets HD carry contacts 5 and 6 whichare included in the lamp energizing circuits for the associated signal. Those circuits, in turn, derivelighting current from any suitable local energizing source that is designated by the terminals plus" and minus.

Looking at any one of the system signals and its pair of control relays HD, it will be seen that:v (l) with relays H and D both picked up the clear lamp G of the controlled signal receives-lighting current over front contacts 5 and 6; (2) with relay H picked up and relay D released the approach"'signal lamp Y is energized with relay H released the stop lamp R receives lighting current over back contact 5. v

In the complete A. P. '3. system of Fig. 1 these indication selector relays HD for the system wayside signals SE and SW are controlled in the manner which the track diagram of Fig. 2 shows. In that diagram the thin horizontal lines that are represented above and below the central tra'ck showing respectively are identified with the westbound signals SW and. with the eastbound signals SE.

In all instances:' (1) the heavy vertical bar at each signal location identifies the pair of horizontal control limit lines emanating therefrom with the signal at the bar location which is on the same side of the track as is the bar; (2) each solid limit line designates that the home control relay H for the line-identified signal is held picked up when all track sections spanned by that line are vacant; (3) each dotted" limit line designates that the ,distant control relay D for the line-identified signal is held picked up when all track sections spanned by that line are vacant; (4) each limit-line arrow that points in, the direction of the associated signal's trafllccontrol (eastbound for each device SE and westbound for each device SW) designates the range within which a track section shunt will release the signal control relay (H or ,D) to which the 'arrowed line applies; and (5) each limit-line arrow that points against the direction of the associated signal's traflic control (westbound for each device SE and eastbound for each device SW) designates the range within which a track circuit shunt will release thesignal control relay (H or D) to which the arrowed line applies.

The eastbound headblock signal SEM (at location I) may well be used to illustrate how the control limit diagram of Fig. 2 is read. For folover front contact 5 and back contact 8; and (3) lowing moves (refer to the limit-line arrows which point eastwardly), Fig. 2 shows that the control range of this signalfs H relay (device HEMat location 11) extends as far east as location HI and that the control range of the signal's D relay (device DE at location II) further extends to location IV; for opposing moves (refer to the limit-line arrows which point westwardly) Fig. 2 shows that the control range of each of the signal's H and D relays extends still further east to location VI, and thus embraces the entire A.

H and D relays be picked up and that signal SEM then show clear. When, however, a westbound traln (see the westwardly pointing limit- -li ne arrows) occupies any portion of the track stretch VII, Fig. 2 directs that the named H and D relays both release and that the eastbound headblock signal SEM-now show stop," in the conventional directional protection manner.

When, moreover, an eastbound train (see the eastwardly pointing limit-line arrows) occupies either of sections I-II and HIII, Fig. 2 directs that the H relay for signal SEM be released and that the named signal again show stop; when the eastbound train vacates sections I-II and 11-111 by moving into section IJI-IV, Fig. 2 directs that .the named D relay only be released and that signal 'SEM then show approach; and

when the eastbound train has moved completely into section IV--V, Fig. 2 directs that the named H and D relays both pick up and that signal SEM once more show "clear. These latter actions accord, quite obviously, with co'nventional principles of following protection.

Reading, by way of further example, the control limit diagram of Fig. 2 on the eastbound inlength IVVI; should show approach after the eastbound train has moved on into track length VIIIIa; and (6) should show clear when the eastbound train has moved further on past location IIIa.

\ From the foregoing it will accordingly be seen that the eastbound and westbound wayside signals SE and SW of the Fig. 1 track.layout are organized into a traffic controlling system that is designed to ofier all of the usual features of A. P. B. protection. When controlled in accordance with the track limit diagram .of Fig. 2, these signals thus permit two'or more trains to follow each other through portions of single track that are between passing sidings and at the same time they prevent a train from entering a single track stretch when that stretch is occupied by another train moving in the opposite direction.

For efiecting this Fig. 2 form of A. P. B, signal control use is made of the coded trackway ap- .paratus which the composite diagram of Figs.

la-lf represents. This apparatus exactly duplicates that which the earlier mentioned Norfolk and Western A. P. B. installation employs and it enables substantially all of the usual signal control line-wires to be eliminated from the system, as Fig. 1 indicates.

The coded track circuit portions of this control apparatus difier somewhat with the positioning of the circuited track sections in the stretch and for the Fig. 1 system these trackway facilities may be grouped into the following classes:

. (1) Track circuitcombinations for the intermediate sections II-II I, III IV and IVV;

(2) Track circuit combinations for the "headblock sections I--II and V-VI; and

(3) Track circuit combinations for passing siding sections such as are indicated at VIIa and VIa-I in Fig, 2.

The track circuit combinations for the intermediate sections II-III, IIIIV and IVV will first bev considered. .These combinations are broadly similar to those which the earlier named Nicholson application Serial No. 382,431 discloses and claims. Each includes two track circuits respectively identified with the two opposing directions of traflic and herein designated as eastbound and westbound.

Both .of these track circuits in each combination include the rails l-Z of the particular track section with which the combination is identified; one is supplied from a given end. ofthe section with normal master code energy which is of a character suitable for controlling wayside signals.

and train carried cab signals and which consists of on period pulses that are separated by fofi period intervals and that recur at one or another of a plurality of distinctivecode frequencies; and

the full section length. Upon interruption of such master energy transmission the feed back I pulses supplied to that other circuit are replaced by specialmaster code energy which consists of recurring pulses that are independently modulated at one or another of a plurality of distinctive code frequencies and that is of a character suitable fior controlling wayside signals and train carried cab signals.

As each of these intermediate track circuit combinations includes the rails I2 of the circuited track section plus cooperating apparatus at each of the two section ends, it is believed that a full and completeunderstanding thereof will result from an examination of the equipment which the Fig. 1 system utilizes at the various locations of track section junction therein.

Apparatus at intermediate locations III and IV As represented by each of Figs. 1c and 1d, the apparatus at each of the intermediate locations IIIand IV comprises: 1) the earlier described eastbound and westbound wayside signals SE and SW; (2) relays HEHEPDE which serve to select the indication that the eastbound signal SE displays; (3) an eastbound track relay TR which is incorporated into the eastbound track circuit for the eastwardly extending section' (which signal SE guards) and which control relays HE-HEP-DE in accordance with the frequency of recurrence of pulses of operating energy that are received from the east section rails; (4) relays HWHWP-"DW which.serve to select the indication that the westbound'signal SW displays; (5) a westbound track relay TRA which is incorporated into the westbound track circuit for the westwardly extending section (which signal SW guards) and which controls relays HWHWPDW in accordance with the frequency of recurrence of pulses of operating energy that are received from the west section rails; (6) a source BXCX of alternating current energy which is incorporated into the eastbound track circuit for the Westwardly extending section and which under the control of a coder relay CTP supplie the west section rails with recurring pulses of "normal master code current; (7) a source BK'CK of alternating current energy which is incorporated into the westbound track circuit for the eastwardly extending section and'which under the control of a coder relay RC supplies the east section rails with off period pulse of feed back" energy at the other normally is supplied from the opposite end of the section with off period pulses of feed back energy which is of a character suitable for registering whether the normal master pulses are or are not'being transmitted through times and with independently modulated pulses of special master code energy at other times;

(8) code transmitters ICT and I5CT which under proper conditions operate the eastbound and westbound coder relays CTP and RC at either a I80 or a I5 pulse per minute code fre- -quency;' (9) eastbound and westbound directional stick relays ES and. WS which form part of the directional protection scheme for the complete A. P. B.system; and (10) devices CCR and SCP which assure a prompt resetting of the track circuit combinations under all conditions of shunt removal therefrom.

The eastbound-westbound? trackcircuit combination for section IIIIV 'will serve to illustrate the organization and functioning of each and every one ofthe intermediate section combinations (II--III, IIIIV and IV-'V) in the Fig. 1 system. Examining the Figs. lc-ld portion of the composite diagram, it will be seen that the master energy source BX-CX at the section east end 1V normally transmits on period pulses of normal master code energy to the eastbound track relay TR at the section west end; that the combined feed back and "special code energy source BK-CK-at that west end III normally transmits off period pulses of feed back en- 5 ergy to the westbound track relay TBA at the section east end; that the eastbound intermediate signal SEIII at the section west end III is controlled by the eastbound track relay 'I'R.

thereatthrough the medium of home and distant decoding relays-HE and DE plus a home repeater device HEP; and that the westbound intermediate signal SWIV at the section east end IV is controlled by the westbound track relay TRA thereat through the medium of "home and i distant" decoding relays- HW and DW plus a 4 home repeater device HWP.

From the Fig. 1 diagram it will be evident that each set of these decoding relays HEDE and HW-DW is supplied with pick-up energy over a pole changing contact 8 of the controlling track relay and by way of a decoding transformer DI and that the decoding relays of the set have response characteristics of the usual "frequency code type. That is, both relays in each-set stay 5 released when the controlling track relay (TR: or TRA) fails to follow code; the home relay (HE or HW) picks up whenever the controlling track relay follows code of either a 75 or a 180 pulse per minute frequency; andthe distant relay (DE or DW) picks up only when the controlling track relay follows code of the 180 pulse per minute frequency.

As the circuit diagrams further show, this selective response by the distant relays DE and DW is, produced by frequency selective units I80DU that are interposed in the relay pick-up circuits in the usual manner, while the necessary rectification of the current which the-decoding transformers DTE and BTW supply to the 40 "home relays HE and HW is effected by track relay contacts 9 arranged as disclosed and claimed by.a copending application Serial No.

210,744 filed May 28, 1938 by Frank H. Nicholson et 8.1., now (U. 8. Patent 2,237,788.

tions of our invention differ from those of the Nicholson application Serial No. 382,431 is in supplementing these home decoding devices HE and DE by the earlier mentioned repeater relays HEP and HWP. In manners later to be made evident those repeater relays perform essential functions: (1) in the control circuits for the systems directional stick relays ES-WS (later to be described); (2) in the'control circuits for the systems reset aiding devices 80? (also later to be described); and (3) in certain j other circuits of the complete A. P. B. organization.

Each repeater relay nnrjand HWP is designed 6 to have a pick-up delay of from 0.3 to 0.4 (or more) second; each of these relays has a pick-up circuit which includes a front contact I. of the controlling decoding device HE or HW; the pickup circuit for each HEP relay further includes a back contact l l of the westbound directional device WS at the same location; each HWP pick-; up circuit similarly includes a back contact I! of the associated eastbound device ES; relay HEP is provided with a snubbing gesistor I which produces a release delay of about 0.25 second; and relay HWP is provided with a first snubb fl resistor 2| which produces a release delay of about 0.25 second and also with a second snub- 45 One way in which the track circuit combinaof a WS contact 65, increases this delay period to between 0.85 and 1.3 second. v

I It will thus be seen: (1) that with WS contact ll closed at its back point, the eastbound device HEP repeats each pick-up and each releasing action of the decoding relay HE by which it is controlled; and (2) that with ES contact released, the westbound device HWP repeats each pick-up and each releasing action of the decoding relay HW by which it is controlled.

in both instances the release delays earlier stated assure: (1) that the controlling relay 'HE (which itself must be somewhat slow in releasreset aiding relay con at the opposite end of the p section.

From Figs; 10-11! it will also be evident that the indication which eastbound intermediate signal SEIII displays is determined by west-end decoding devices I-lEP-DE through the medium of the earlier named contacts 56 and that the indication which westbound intermediate signal SWIV displays is similarly controlled by eastend decoding devices HWP-DW. In each instance, .quite obviously, the controlled signal shows: (1) clear when the associated track relay (TR. or TBA) follows code at the 180 rate; (2) approach when the track relay follows code at the '75 rate; and (3) stop when the trackrelay fails to follow code.

' Eastbound intermediate track circuits Looking at the complete track circuit combination for section III- -IV of Figs. lo-ld, it will be seen that the normal master" code energy which is supplied to the section rails from source BX -CX at east location IV is modulated or periodically interrupted under the coding con-- trol of code transmitters I80CT'I5CT at that east location. The contacts I80 and [5 with which these andall other transmitters in the system are provided operate in conventional manner in that they repeatedly pick up and release at the respective frequencies of 180 and times per minute.

One or'theother of these transmitter contacts 180-l5 at location IV operates sectiOn'III IVs master coder relay CTR over a local driving circuit which includesa conductor l3. 'This sooperated coder device CT? (and all other devices of like designation, in the system) is provided with contacts ll-li which, depending upon which of the transmitter contacts I and I! is included in its driving circuit, recurrently pick.

up and release at one or the other of the two code frequencies earlier named. When picked up these contacts [i -I5 connect the rails of section III-1V with source BX-CX and thereby produce a normal master on" period; when released these contacts transfer the rail connection to track relay'l'ltl l and thereby produce a normal bing element 25. which, under. released conditions 75 master off period. Included in both of the connections just named is the usual track transformer 'I'IE.

Assignment of the driving circuit for this location IV coder device CTP to one or the other of the code transmitter contacts l80'|5 at the same location is controlled by the eastbound decoding relay HE for section IV--V tothe east. Acting through the repeater relay HEP at location IV, that eastbound decoding relay utilizes contacts I'l-I8 of device HEP together with contacts |920 of associated devices ES and HWP to select between the transmitter contacts I80 and 15.

When (as Fig; 1d shows) devices HEHEP at location IV are picked up, the control of coder relay CTP is assigned to transmitter |80CT and that coder relay then is caused to produce a normal master energy code consisting of I80 on period pulses per minute; when, however, the relay driving circuit is transferred to transmitter 150T, relay CTP is caused to produce a normal master energy code consisting of 15 on period pulses per minute.

In flowing westwardly over the section rails to west location III, the recurring pulses of this .normal master code energy (from source BK- CX) are impressed upon the master track relay TR by way of track transformer TTW, back contacts 22'23 of an impulse relay RC, and a rectifier 24. Under vacant section conditions, accordingly, this track relay TR is caused to pick up and release its contacts 8-9 in step with the operations of code producing contacts I4-|5 of the east end relay CTP. Bythe associated decoding relays HEDE-HEP that response is, in turn, translated into appropriate indication selections for the eastbound wayside signal SEIII.

Thus, if at least one signal-block section to the east of location IV is vacant, the driving circuit for location IV relay CTP will be assigned to the code transmitter contact I80, the pulses of normal master energy, suppliedto section III-IV will recur at the I80 code rate, the eastbound track relay TR at location III will respond at that I81] rate; the associated relays HEHEP-DE will all be picked up, and the eastbound signal SEIII will now show clear.

Should an advance eastbound train be in the signal-block section just-east of location IV, the driving circuit for location IVs relay CTP will be assigned to the code transmitter contact 15, the pulses of normal master energy impressed upon section III-'IV now will recur at the 15 code rate, the eastbound track relay TR at location III will respond at that 15 rate, the associated relays HE-HEP only will be picked up, and the eastbound signal SEIII will show approach.

Should, finally, the advance train be in section IIIIV, the eastbound signal SEIII will display stop. This, of course, resultsfrom the usual deenergization of track relay TRA and the consequent release of eastbound decoding relays HEDE at location III.

. for all eastbound train moves through the A.P.B. stretch.

Westboundintermediate track circuits A corresponding control of the westbound wayside signals SW, and also of train carried cab signals (not shown), is effected through the feed back-special master track circuit appa- I ratus that earlier was referred to as supplementing the normal master organization just described. For intermediate track section In -IV of Fig. 1, this apparatus includes the Westbound the westbound track circuit source BKCK at the section west end III. vDuring the off periods of, the west end received normal master code energy, the before mentioned coder relay RC the section III-IV rails over the front points of its contacts 2223 and thereby supplies those rails with the pulsed feed back energy by which the east end track' relay TRA at location IV is operated.

This location III coder relay RC (and all other devices of like designation in the system) closely resembles a device which Herman G. Blosser Reissue Patent No. 21,783 (granted April 29,

25 1941) discloses at IR in a coded feed back section III--IV are connected with the east end track relay TR; when, however, suitable pick-up current is supplied to the relay these contacts pick up and transfer the rail connection to the east end supply source BKCK.

Under vacant track conditions, this pick-up current is derived from an output winding 26 of the location III decoding transformer DTE and transmitted to relay RC through a transformer 21. The primary of this transformer is connected with winding 26 at all times; the secondary of transformer 21 is connected with the winding of relay RC over a front contact 28 of eastbound decoding relay HE, either a front contact 29 of the westbound directional stick. relay WS at location III or a front contact 30 of the westbound decoding repeater relay HWP for the section to the west of that location, and a conductor 36. Relay RC responds only to positive polarity pick-up energy (Which makes the right terminal of its winding positive with respect to the left terminal) and each release of the eastbound track relay TR causes decoding transformer DTE to induce in winding 26 a pulse of such positive polarity potential. When the just described secondary circuit for transformer 21 is complete, each of those positive pulses is transmitted to relay RC and produces a momentary pick-up on the part of contacts 22-43 thereof.

Such pick-up, as already pointed out, connects the rails of section IIII'V with the west end source BKCK over a circuit which includes the usual track transformer TTW at location III. This connection causes a short pulse of 5 feed back energy to be supplied to those rails.

Each of these pulses coincides, under the con-' ditions just described, with an oif period of the east end supplied normal master code and hence is transmitted over the section rails tothe east location IV.

There each of the thus transmitted pulses of feed back energy is impressed upon the westbound track relay TRA. Such impression is by r way of transfonner 'ITE, back contacts l4l5 d of device CTP and a rectifier 3| it causes, quite track relay TRA at the section east end IV and at west locationIII connects this source with obviously, this east end track relay TRA to pick up its contacts 8-9 in step with the "off period pick-ups of'the west end coder relay RC.

For the purpose of equalizing the pick-up and release times of the so operated westbound track relay TRA, its pick-up circuit is supplemented by a stick circuit which prolongs each of the re-' lay pick-ups for the full duration of the 0115" period during which the pick-up occurs. This stick circuit includes a back contact 33 of the master coder relay CTP and a front contact 34 of the track'relay; it is supplied with energy over either a front contact 35 of the eastbound decoding relay repeater HEP for the next section to the east or the frontcontact I! of the eastbounddirectional stick relay ES at location IV; and it functions in the same manner as that disclosed and claimed by Patent vNo. 2,172,893 which issued to Edward U. Thomas on September 12, 1939.

Such response by section IIL-IV's westbound track relayTRA to "oif period pulses of feed back energy received from the section west end 111 registers at the section east end IV the fact that pulses of fnormal master code energy there impressed upon the section rails are by those rails being transmitted completely through to and received at the west location III.

During such registration the westbound track relay TRA at location IV operates at the code frequency that is set by the normal master energy pulses with which section III-IV is sup- This vacant stretch" holding does not, how-.

ever, prevent signal SWIV from showing the desired advance traffic responsive indication upon the approach of a westbound train. Such approach releases relays HE--HEP at location IV and thereby discontinues (through the medium of directional protection facilities later to be described) all transmission of "normal master energy pulses to the west location III. That discontinuance releases relays HE-HEP at location 111 and thereby causes the relay RC thereat to operate not as an impulse device for the supply of feed back pulses during the master code oi I periods but instead as a repeater for one of the west end code transmitters CTI80 and CH5.

During such operation, the trackway energy supplied at west location III (from source BK-CK over front contacts 2223 of device OR) is modulated independently of the master code being produced at east location IV. To designate this independently modulated energy the earlier announced term of special master" code will be employed.

During these conditions of special master code supply, the driving circuit 36 for location III r'elay R13 is set up over one or the other of front contacts 29 and 30 of devices WS and HWP at the same location, back contact 28 of the eastbound decoding relay HE at location HI, conductor 32, and contact ll of the repeater device HEP for that eastbound decoding relay. This driving circuit includes selector contact 20 of the westbound decoding repeater relay HWP for'the track section to the west of location III. When picked up (at a timewhen devices HE and HEP are both released) this selector contact assigns the driving circuit for relay RC to the code transmitter IIOCT (contact I00) at the same location; when released (under released conditions of devices HE-HEP) it transfers the circuit con-. nection to contact 15 of the code transmitter If at least one signal-block section to the west of location 111 is vacant, the control for location III relay RC will be assignedto the code transmitter contact I80, the pulses of special master" energy supplied to section I1I--IV will recur at the 180 code rate, the westbound track relay 'I'RA at location IV will respond at that 180 rate, the associated relay HW-HWP-DW will all be picked up (contact I1 is now"released), and the westbound signal SWIV will now show clear.

- Should an advance westbound train occupy the signal-block section just west of location 111, the control for location 111 relay RC will be assigned to the code transmitter contact 15, the pulses of special master energy impressed upon section III-IV now will recur at the 75 code rate,

a the westbound track relay TRA-at location IV will respond at that '15 rate, the associated relays HW-HWP only will be picked up, and the westbound signal SWIVwill show "approach."

Should, finally, the advance train be in section IIIIV, the westbound signal SWIV will display stop." This, of course, results from the usual deenergization of track relay TRA and the consequent release of both of the westbound decoding relays HW-DW at location IV.

The combined feed back and special master" track circuit organization just-examined for intermediate section III-JV is, therefore, effective to control both the westbound wayside signal SWIV and train carried cab signals (not shown) in the usual automatic block system manner and when expanded into the complete A. P. B. system of Fig. 1 it thus provides the desired following protection for all westbound train moves through the A. P. B. stretch.

Directional protection in the Fig. 1 system In order that a train entering either, end of the A. P. B. stretch of single track will automatically establish its own directional protection therethrough, the complete system of Figs. la-l/ includes facilities whereby advancement of the leading vehicle of the train past the entering headblock location (I or VI of Fig. 1) successively conditions the opposing track circuits ahead in such manner as to set the signals for opposing traffic at stop."

Aiding in this successive conditioning are the directional stick relays ES and WS that previously were referred to as forming a part of the equipment at each of the intermediate locations 111 and IV.

In the organization which Figs. lo-ld illustrate, bothof the relays in each ES-WS set are deenergized and stay released as long as the A. P. B. stretch of single track remains vacant. Upon movement of an eastbound train through the stretch the normally released eastbound relay ES at a given intermediate location picks up when the leading vehicle of the eastbound train first gets about 1000 feet from that location and so staysruntil the trailing vehicle of the train clears the east end of the section of which the HEHEP and the pick-up circuit for relay ES given location marks the west end. Similarly, upon movement of a westbound train through the stretch the normally released westbound relay WS at a given intermediate location picks up only from the time that the leading vehicle of the westbound train first gets about 1000 feet from that location until the trailing vehicle of the train has cleared the west end of the. track section to the immediate west of the location.

This Fig. 1 organization of the directional stick relays is the same as that which a copending application Serial No. 386,633 filed by us on April 3, 1941, discloses and claims. In that organization the two devices ESWS at each intermediate location are provided with a transformer unit EWS which supplies pick-up current toone or the other of those devices upon each approach of atrain.

Each of these intermediate-location units EWS has a primary winding 40 that forms part of: (1) the'circuit through which normal master code energy is supplied to the westwardly extending track section upon the approach of an e'astbound train; and (2) the circuit through which special master code energy is supplied to the eastwardly extending track section upon the approach of a westbound train.

Looking, for example, at unit EWS at location IV, it will be seen:- (1) that the first named circuit extends fromnormal master source terminal BX, through contact l| of a relay OCR, one or the other of contacts |80a and a of code transmitters CT! 80 and CT15, code selecting contacts 4l-42 of relays HWPHEP, the units primary winding 40, a series win-ding E of the unit, conductor 43, front contact I4 of devic CTP; the primary of section IVIIIs track transformer TTE and front contact i5 of device CTP back to normal master source terminal GK; and (2) that the second named circuit extends from special master source terminal BK, through one or the other of code transmitter contacts l80aF-15a, the units primary winding 40, a series winding W of the unit, conductor 44, a back contact of relay HE, front contact 22 of device BC, the primary of section IVVs track transformer TTW and front contact 23 of device RC back to special master source terminal CK.

Inductively coupled with this primary winding 40 of each EWS unit is a secondary win-ding 38 which has induced therein a potential that is proportional to the rail-energizing current which winding 40 transmits. This secondary winding feeds into a full-wave rectifier 39 which renders the alternating current potential thereof unidirectional.

is broken at contacts 48-49 of devices HW' HWP. Under these vacant track conditions, therefore, the directional stick relays ES and WS at location IV both stay released, as shown.

When, however, an eastbound train comes into section III-IV, relays HWHWP at location IV drop and thereby complete (over contacts 4849) a pick-up circuit for location IVs eastbound directional relay ,ES. This circuit may be traced from the positive terminal of rectifier 39 through conductor 5|, a back contact 52 of device WS, back contact 48 of device HW, back contact 49 of device HWP, front contact 41 of device HEP, conductor 53, the winding of relay ES and conductors 54--55 back'to the negative terminal of rectifier 39.

At first the trackway current which the now shunted section III-IV draws through unit EWS is insufficient to pick up relay ES over the circuit just traced. As, however, the eastbound trainnears location IV this current gradually rises and when the closeness of train approach is reduced to about 1000 feet, relay ES picks up.

Further advances of the train toward location IV I of device HE establishes for relay ES a stick circuit which continues that relay picked up as long as any part of the eastbound trainremains in section IVV. That stick circuit is completed before device HEP breaks the original ES energizing circuit by its release of contact 41; it

may be traced from a positive supply terminal through back contact 51 of device HE, a front contact -58 of relay ES, an impedance 59, conductor 53, the winding of relay ES, and conductor 54 back to a negative supply terminal.

When the eastbound train leaves section VIV, relays HE-HEP at location IV again pick up and respectively: (1) release the directional stick relay ES thereat by breaking its stick circuit at contact 51; and (2) condition relay ES for response to another eastbound train by setting up its pick-up circuit at contact 41.

Location IVs westbound directional stick relay WS will be seen to operate in a comparable manner. Upon entry of a westbound train into section IVV a pick-up circuit for that relay is completed by the dropping of relays HE-HEP which accompanies that entry. That pick-up circuit may be traced from the positive terminal of unit EWSs rectifier 39' through conductor Fig. 1d. With both of the there adjoining track section IVIII and IVV unoccupied, the rail supply current that passes through unit EWS is insufficient to produce pick-up on the part of either of relays ES and WS. Under such conditions, moreover, the pick-up circuit for-relay WS is broken at contacts 46-41 of devices 5|, a back contact 60 of device ES, back contact 46 of device HE, back contact 41 of device HEP, front contact 49 of device HWP, conductor 6|, the winding of relayWS, and conductors 54--55 back to the negative terminal of rectifier 39. v

At first the trackway current which'the now shunted section IVV draws through unit EWS is insufficient to pick up relay WS (over the circuit just traced). As, however, the westbound train near location IV this-current gradually rises and when the closeness of approach is reduced to about 1000 feet, relay WS picks up. Further advances of the train toward location IV cause, in a manner which our copending application Serial No. 386,633 more fully explains.

8 aasaaaa II-IILIlI-IV, and IV-V encounter diificulty this picked up condition of relay WS to continue. As the westbound trainadvances past location IV, relays HW and HWP thereat successively drop in the order named. By this action a constick circuit which continues that relay picked up as long as any part of the westbound train remains in section IV-III. That stick circuit is completed before device HWP breaks the original WS energizing circuit by its release of contact 49; it may be traced from a positive supply terminal through front contact H of relay WS, conductor 63, back contact 62 of device HW, an impedance conductor GI, the winding ofrelay WS and conductor back to the negative supply terminal.

When the westbound train leaves. section lV-lII, relays HW-HWP at-location IV again pick up and respectively: (I) release the directional stick relay WS thereat by breaking its stick circuit at contact 62; and (2) condition relay WS for response to another westbound train by setting up its pick-up circuit at contact 49.

For enabling each eastbound train that enters the Fig. I stretch at the west ,end I thereof to deenergize' the westbound track circuits in advance and thereby put the westbound signals SW for the stretch at stop, each of the just described westbound directionalstick relays WS is provided with a knockdown contact 29. This contact is included in the driving circuit of the westbound coder relay RC for the track section to the east and it therein parallels the earlier described contact of the westbound decoding repeater HWP.

By'preventing the aadvancefeastwardly extending sections of the stretch from receiving feed back" energy '(from source BK-CK) during the passage of eastbound trafllc through the stretch, thesecontacts 29-30 of the system relays WS-HWP provide eastbound directional protection of the customary character; in addition the contacts 29 assure that all westbound train moves through the stretch will provide their own following protection. More detailed examination of both of these actions will be undertaken later. For enabling each westbound train that en ten the east end of Fig. I stretch to deenergize the eastbound track circuits ahead and thereby put the eastbound signals SE for the stretch at stop, each of the just described eastbound directional stick relays E8 is providedwith a knockdown :contact [9. 'Ihis contact is included in the driving circuit of the eastbound" coder relay CI? for the track section to the bound directional protection of thecustomary character; in addition the contacts [9 assure that all eastbound train moves through the stretch will provide their own following protection. these actionswill be understaken later.

Reset aiding devices CCR and SCP Under certain conditions the track Y circuit combinations for the intermediate sections More detailed examination .01 both of in shifting from their westbound control ,supply of special master code energy back to their vacant section supply of feed back energy. Such a shifting action will be referred to as resetting and the problems which are incident thereto are in part solved by the inventions of the earlier named Gilson and Allison applications Serial Nos. 386,642 and 386,615.

As the Gilson and Allison specifications rather fully explain, these reset problems arise out of the fact that at times the pulses of .normal master code energy which are supplied (from source BXCX) to the east end of a section may coincide with and be opposed by the pulses of-special master" code energy that are supplied (from source BKCK) to the west end of the same section. g

Looking, by way of illustration, at section III-IV of the present application, it will be seen that a shunt placed across the rails of this section continuously releasesboth the eastbound and westbound track relays TR and TRA therea for; that this continuous-release of track relay TR. at location III transfers (at contacts 28 and of devices I-lE-I-IEP) the control of west end coder relay RC from the track relay TR to one of the code transmitters I8IICT15CT at the same location; and that thistransfer causes relay RC to be driven by one of the named location- HI transmitters for the purpose of supplying (from source BK-CK) pulses of special master code to the section west end. As long, quite obviously, as the section rails remain shunted the supply of these special master pulses continues.

Upon removal of the shunt from the rails, moreover, these recurring pulses of special master code energy continue to be impressed upon the section west end III andhence are transmitted over the section rails toward the east location At that east location, meanwhile, the section rails also are supplied with recurring pulses of Normal Master code energy which -flow over the rails toward the west location III. Due to the resulting clash of these oppositely flowing pulses, the "normal master energy may be prevented from getting through to and operating the west end track relay TR and the special master energy may be prevented from getting through to and operating the east end track relay TRA.

This prevention falsely holds the sections eastbound and westbound signals SE and SW at ness may decrease to the point of substantial disappearance.

Such, for example, is the case upon: (1) ordinary clearance'of the section east end IV by an eastbound train; and (2) ordinary clearance of the section west end III by a westbound train. In'each of these instances the energy pulses that are supplied to the train leaving end of the section recur at the IS code rate, the energy pulses that are supplied to the opposite end of the section recur at the I code rate, and resetting is prompt because timesfrequently occur when the energy supplied toeach end of the section canget through to and operate the track relay at the opposite end thereof.

The mechanics of such self-eifected reset are as follows. Falling in step with the off periods of the west-to-east flowing special master. code, the east-to-west flowing pulses of normal master energy reach and operate track relay TR; that operation picks up eastbound decoding relay HE at location III; that pick-upv transfers (at contact-28) the driving circuit for coder relay RC from code transmitter'lBUCT to impulse winding 26 of decoding transformer DTE; that transfer causes the coder relay RC to pick up upon each release of the track rela'y TR; and that action restores the track circuit combination to the desired coded feed back form of vacant section operation.

Under certainother conditions; however, the two clashingcodes do have the same frequency of pulse recurrence and in that event reset of the track circuit may be objectionably delayed. As an example of such other conditions, consider the following situation.

With the track stretch initially vacant, a train comes into section III-IV not by way of either end thereof but at an intermediate point therein from a spur siding (not shown).- The section to the east of location IV being vacant, the east end coder relay CTP is being driven by the east end transmitter IBUC'I' and the section rails now are receiving (from east end source 'BXCX) 180 pulses per minute of normal master code energy. The section to the west of location 111 also being vacant, west end coder relay RC then is being driven by west end transmitter IBOCT and the section rails 'now also are receiving (from west end source BK-CK) 180. pulses per minute of special master" code energy.

Should the train now leave section III-IV not by passing out of either end thereof but by.

way of the same spur siding (not shown) over which it entered, the pulses of 180 codeenergy that are fed to the section from opposite ends will either: (1) 'interfit and allow both the west and the east end track relays TR and TRA to be energized in a manner which produces immediate reset; or (2) clash and prevent each of these track relays from receiving operating energy from the opposite end of the section. It is in the latter event that one of the earlier stated problems of track circuit reset occurs. a

This will be referred to as the problem of initial reset. In accordance with the Gilson invention this initial reset. problem is solved by supplementing the code supplyapparatus at one end of each circuited section by a code converter relay CCR which during and immediately fol-, lowing each shunt of the section rails recurrently interchanges the on and off periods of the coded energy which is impressed upon those rails at the converter location. Upon restoration of the section to its normal unshimted-condition,

stores the track circuit to the desired coded feed back form of vacant section operation.

In the complete A. P. B. system of the present invention; the west end of each of the intermediate track sections IIIII, lII-IV and IVV is equipped with one of Gilsons code converter relays CCR.- This -'relay carries contacts lll0-l0l which respectively are included in: (1) the "special master code driving circuit (one or the other of code transmitter contacts l8il-'|5,and back contact 28 of device HE) for the impulse relay RC at the same location; and (2) the primar energizing circuit (one or the other of code transmitter contacts IBM-15a and transformer winding 4%) for the directional stick relay pick-up unit EWS atthe same location.

When these contacts IOU-IN are released (as shown), element I00 connects the RC relay driving circuit with the back point of whichever of the two transmitter contacts I80 and 15 is included in that circuit; when, however, contactsv I00--l0l are picked up the RC relay driving circuit is shifted to the front point of the selected transmitter contact. Each shift, therefore, in the position of contacts l00-|Ill causes the coder relayRC to-interchange the on and the off periods of the special master code energy which is supplied to the west end of the associated track section.

' The operating characteristics of these code converter relays CCR for the Fig. 1 track sections IIIII, III-IV and IVV preferably duplicate those of the correspondingly identified devices of the Gilson application. In that event the contacts loll-ll of each relay normally occupy one or the other of their two positions continuously. When, however, pulsed driving current is supplied to the operating mechanism or winding of the relay (for details see Gilsons Fig. 3) these contacts lll0l0l then shift their position at. intervals of every eight seconds.

Supplying each of these CCR relays with such pulsed driving current at proper times is anoperating circuit which includes a contact 15b of the code transmitter I5CT at the relay location, a back contact 58 of the eastbound directional stick relay ES at the same location, and

a back contact 51 of the eastbound decoding relay HE for the eastwardly extending track section. As in the Gilson organization, the purpose ofthe stick relay contact 58 is to prevent needless operation of the converter relay CCR during certain eastbound train moves. y

Each just described converter relay CCR accordingly holds its contacts IOU-"ll continuously in the same position as long as either of vices HE'ES-. become released, the controlled relay CCR receives pulsed operating current over code transmitter contact 15b and the CCR contacts l|l0'l0l thereby are caused then to shift their position every eight seconds.

In examining how each of these CCR relays assures'a prompt initial reset of the track circuit that extends eastwardly therefrom, attention will, by way of illustration, 'be directed to device CCR at location III. and to the track section III-IVwith which that device is associated. Under vacant conditions of the Fig. 1

track stretch, the track circuit combination 'for* this section IIIIV is operating in the normal coded feed back manner; the eastbound directional stickrelay ES at location 111 is released;

the eastbound decoding relay HE at the same location is picked up; and the west end code energy therefor.

a resetting of the track circuit and restores the converter relay CCR for section IIIIV consequence, maintained inactive.

Assume, now, that the rails of section IIIIV become shunted at a time when the section to is. in

' the west of location III is vacant and when the .section to the east of location IV also is vacant. This shunt drops the eastbound track relay TR.

"consequence, the energy of those master pulses type must overcome arises out of the effect on a particular section of actions which take place in one of the adjoining sections of the A. P. B.

stretch. This effect is to be distinguished from The release of relay HE at location III which produced that transfer causes contact 51 to complete the operating circuit for the code converter relay CCR. That completion, in turn, allows recurring pulses of driving current to reach (over the front point-of code -transmitter contact 15b) device CCR. and thereby causes that device to shift the position of its contacts every few seconds. Each of these shifts effects, in the manner earlier explained; an interchange in the on and the off periods of the west end supplied (over contacts 22-23 of coder relay RC) special master" I80 code.

.At the east end IV of the section, meanwhile, the driving circuit for the master coder relay CTP continues to be assigned to code transmitter .I80CT, and, in consequence, 180 pulses per minute of normal master code energy now also are impressed upon the rails of section lII-IV.

Assume next that the rail shunt is removed from section IIIIV by some method other than train movement out of one end of the section. The stated requirement might, for example, be met by passage of a train vehicle out of the section by way of a spur siding (not shown). At the instant of such shunt removal the pulses of east end supplied normal master I80 code energy are net 'and opposed by the pulses of fall in 'step with the special master 011'v periods, the energy of those normal master .pulses gets through to track relay TR. at location III in the desired manner. In responding that relay discontinues (by picking up relay HE) the supply of special master code energy and substitutes off period pulses of feed back This substitution constitutes desired coded feed back form of vacant section operation thereto. Under that condition, of course, the now picked up relay HE at location llI'interrupts (at contact 51) the operating circuit for the west end code converter relay COR and thereby restores that relay to its normally inactive state. I

In the event, however, that the pulsesof normal master I80 code energy initially do coincide with the opposing pulses of special master I80 code energy, then relay TR at location HI remains continuously deenergized and the track.

circuit is prevented from resetting. Such prevention persists, however, only until the code converter relay CCR. at location III next shifts the position of its contact-IIOI.

By that shift the special master code on and off periods are interchanged to a positioning' wherein the normal master on period pulses do fall within the off period intervals of the opposing special master code. In

the initial reset functions which the just 'described code converter relays CCR perform and it results in what will be termed a cascading of the reset operation requirement from one section to another.

As the Allison application Serial No. 386,615 very clearly brings out, such cascading is peculiar to A. P. B. systems wherein track circuits of the type herein considered are includedand in the absence of cascade preventing means the attendant section-to-section transfer of the reset requiring conditionsmay in certain cases cascade itself back and forth from one end of the A. P. B. stretch to the other several times before permanent reset is effected.

In accordance with the Allison invention this cascading difficulty is overcome by: (1) supplementing the normal master code supply apparatus of each cascadable track section in the A. P. B. stretch by an auxiliary device FL or BL (not shown herein) which when operated makes a single interchange in the on" and "011 periods of the normal master code energythat is supplied to the section rails at the device location; and (2) ,arranging that this device will delayedly operate in response to each restoration of the location adjoining track section to its normal coded feed back'form of vacant section operation.

In the track v circuit combinations of our complete A. P. B. system Allison's just described code period interchange devices (FL or BL) are replaced by auxiliary relays SOP One of these relays is installed at the east end of each of the intermediate track sections II-III and IIIIV and it there performs functions similar to those of the Allison device plus certain additional ones later to be made evident.

In the form shown at each of locations II and III, this auxiliary relay SCP carries.a pair of contacts 6I68 which normally are released, as

from a positive supply terminal, through front contact 51 of device HE at the relay location, conductor 69, front contact 10 of device HW, contacts II and 12 of devices HWP and HEP, conductor I3 and the winding of relay SCP back to the negative supply terminal.

Each such completion picks up the SCP relay and thereby causes: (1) contact 61 to connect the associated'master coder relay C'I'P directly with the plus terminal of its control source; and (2) contact 68 to connect the front point of this CTP relays contact ll directly with terminal BX of the normal master trackway source." During these connections: (1) relay CTP is held continuously picked up; and (2) source BX-'-CX supplies the rails of the westwardly extending track section with uncoded or steady normal master energy.

duration in excess of 0.4 second and is, of course,

terminated by the release of the controlling relay SCP. J

Before examining when and for what purpose these auxiliary relays SCP pick up and release, it may be pointed out that two important functions are performed by the just described single code pulse energy that the relays govern. These functions are: (1) prevention of reset cascading from one A. P. B. track section to another; and (2) making more prompt and positive the initial reset of 'track'circuit combinations for individual sections in the system.

The last named function will be considered first. To explain it the track circuit combination for section IIIIV will again be examined. In this combination (and in all others of corresponding intermediate character), the earlier discussed west end code converter relay CCR at location III is supplemented by the single code pulse. relay SCP thatjs installed as just described at the section east end IV.

That supplement, however, in no.way interferes with the earlier explained functioning of the west end relay CCR; whenever devices HE and ES at location III both are released that relay shifts its contacts IIOI at intervals of about eight seconds and by thus interchanging the on and off periods of the special master code energy that is supplied to the west end of the section it assures an initial reset of track circuit IIIIV sometime within the eight second interval. I What the supplementing relay SCP at the section east end IV does do is to: (1) pick up upon the first response of the westbound code master-code or feed back energy that is received from the section west end'III; and (2) While so picked up, relay SCP causes single code pulse" energy to be impressed upon the east end of section IIIIV. The duration of that steady energyimpression (in excess of 0.4

second as aforesaid) is suflicient to overlap a full ofi period of any opposing code (eitherv special master or feed back) that is supplied to the section west end III. During that overlapped oi'f period the single pulse energy from' the east location IV reaches west location III without interference and there provides a ve y filtlve pick-up for the eastbound track relay That positive pick-up by the west end track relay TR may occur before, during, or after the "initial resetting of track circuit IIIIV which the code converter relay CCR therefor by itself effects. When before, it independently transfers (at contact 28) the control for location IIIs coder relay RC to the impulse transformer 21 and thereby provides positive reset more quickly than could relay CCR; when during, it guards against a subsequent reset loss due to too weak an original pick-11p of relay TR and thus renders the .70 detecting relay HW thereat to either special impress single code pulse energy upon the section east end during such pick-Pup. This pickup by relaySCP is produced in the following manner.

At the instant of the named HW-relay response, the westbound code detecting and re-,

peater relays I-IW and HWP at location IV both are released (assuming that section IIIIV previously was shunted) while the eastbound code detecting and repeater relays HE and HEP at the same location both are picked up (assuming that section IVV now is vacant). As the first pulse of BK-CK energyfrom the west reaches track v HW, back contact II .of relay HWP and front contact I2 of relay HEP.

initial reset more positive and lasting; and when after, it in no way interferes with the earlier restored "coded feed back form of vacant section operation for. track circuit IIIIV.

The function of the auxiliary relays SCP in preventing cascading of the reset operation requirement from one section to another will next be considered.

One pressing need for such prevention is encountered during eastbound train moves through the A. P. B. stretch. Assume, for example, that an eastbound train which entered the stretch of Fig. 1 at the west location I has advanced to the point in the stretch where it is about to leave the east end of section IVV.

While the train is at this point, relay ES at location- IV is up; relays HE-HEP at the same location are down; and the east end of section IIIIV is being supplied with fnormal master c ener y. This supply results from the master coder relay CTP at-location IV being driven by one of the code transmitter contacts l8ll-.-'I5 at the same location over a connection there-. with which includes front contact I9 of relay ES. As, now, the train moves out of-section IVV, relay HE at location IV picks up; relay ES at the same location very quickly releases; and after a delay of about 0.4 second relay .HEP picks up. During this delay interval the driving circuit for'the master coder relay CTP at location IV is broken at'the as yet unpicked up contact ll of relay HEP.

That breaking, quite obviously, may happen to fall at any point in the cycle of normal master code for section*IIIIV that relay CTP is producing. If it falls at the beginning of an off period; the interval of no energy supply is extended only slightly beyond 0.4, second. This extension not greatly exceeding the off-period length for I5 code, no objectionable efiects are produced at location III.

If, however, the CTP driving circuit break (by contact I9) occurs at the very end of anormal master "off period, the interval during which no energy is supplied to the east end of section IIIIV equals the off code period time plus the 0.4 second pick-up delay for relay- HEP. At

location III the resulting prolonged release of track relay TR. allows eastbound code detecting relay HE to drop its contacts. Even though momentary, the. duration of this drop proves suflicient to effect the release of repeater HEP.

By that release contact ll breaks the driving circuit for the master coder relay CTP at location III and thus causes the track circuit combination for section IIIII to lose its reset; and

by a similar sequence of actions succeeding in-' termediate track sections (not shown in Fig. 1)

' use is made of ourearlier described single code pulse relays SCP at the intermediate section Apparatus for west headblock section III Description now having been given of the intermediate location positions of our new and imeast ends. Again examining device SCP at loca- 1 tion IV, its functioning upon the earlier described eastbound train movement out of sections IVV will now be reviewed.

As the train clears location V, normal master code energy is again transmitted to location IV.

There track relay TR responds and picks up eastbound code detecting relay HE. At theinstant of this pick-up by relay HE, the westbound code detectingrelay HW at location IV is picked up (assuming that section IIIIV was originally reset) and the eastbound decoding repeater IE2? at the same location is released (due to the previous shunt of section IVV) Hence, the original pick-up by contact 51 of this location IV relay HE is followed about 0.4 second later by a pick-up of contact H of the associated slow acting repeater relay HEP..

During that 0.4 second interval the location IV relay SCP is picked up over front contacts 51 and 10 of relays HE and HW and back contact 12 of relay HEP.

While so picked up, relay SCP causes single code pulse energy to be impressed upon the east end of section III--IV. The duration of that steady energy impression (in excess of 0.4 second as aforesaid) is sufficient to overlap a. full of! periodof any opposing code (either special master or feed back) that issupplied to the section west end 111. Itseifect is (as before) to provide a very positive pick-up for the west end track relay TR. 1

That positive pick-up by track relay TR at location III guarantees that the track circuit combination for intermediate section lII IV will under no circumstance lose its reset upon the earlier described departure of an east-bound train from the adjoining intermediate section rv-v to the east; A similar guarantee against.

loss of reset in the intermediatesections to the west of section III-IV is, in turn, made by the single code pulse relays. at the east ends of those west sections. V

From the illustrative condition of resetloss "cascading which has just been described it will .be seen that the single code pulse relays SCP of the Fig. 1 system effectively safeguard each and every intermediate track section therein from having its coded feed back form of vacant section operation 'objectionably interfered with by actions which take place in one of the adjoining sections. 7

Such further tendencies (not described herein) toward reset cascading as may be set up during operation of the complete A. P. B. system are found also to be overcome by the novel reset aiding facilities of our invention. In the earlier mentioned Norfolk and Westerns commercial inheadblock and siding leaving signals SEM and SES earlier described as being installed at location I; (2) westbound siding entering signals SWII earlier described as being installed at location II; (3) home relays HEM and HES for respectively controlling signals SEM and SES; '(4) a distant relay DE which aids in the control of both of those signals; (5) .home and 'distant control relays HWI and DW for signal SW11; (6) track circuit and associated wayside facilities for governing the just named signal con- I trol relays in accordance with traflic conditions in and beyond the ends of section 1-11 and for supplying cab sign'al control energy to the rails of that section; (7) a track switch W for selectively connecting the rails of passing siding PSI with those of the main track I2; (8) switch repeater relays NWP-RWP for causing the signal control relays to check and respond to changes in the position of switch W; and (9) code transmitters I 800T and HOT which form a part of the track circuit facilities for headblock sectio'n 1-H and which also are utilized by the track cirguit facilities for the east and west adjoining secions. v

The earlier described shortness of this west headblock section III (length seldom greater than two or three hundred feet) permits :devices Figs. la-b a number of such connections are illustrated.

The track circuit portions of the complete sig-' nal control combination which is represented by that diagram comprise: (1) apparatus connected with the west end 11 of the eastwardly adjoining track .section 11-111; (2) apparatus connected with the east end I of. the westwardly adjoining section (which corresponds to Ia-VI of Fig. 2); and, (3) apparatus connected with the rails of headblock section III.

Looking first at the location II apparatus for track circuit IIIII that apparatus will be seen to comprise elements .'I'I'W, RC, BX-CX, TR. n'rs, Imps, l8015C'I' and CCR which-are organized in substantially the same manner as at each 'of locations 111 and IV (for sections Inf-IV and IVV) repeated. Instead it will suflice to observe: (i)

that the code-selector contacts l82ll and 42- for the I special normal" energy (from source BK-CK) control and supply circuits 32 and 44 I are carried by the home and "distant control relays HWI and DW for the siding entering signal SWI I; and (2) that the eastbound directional The apparatus for the west 

